1. Field of the Invention
The present invention relates to an organic semiconductor thin film, and an organic semiconductor device and an organic field effect transistor both including the organic semiconductor thin film.
2. Related Art
In recent years, an organic compound having semiconductor characteristics has attracted attention. Among the organic compounds, a polyacene compound such as pentacene and tetracene has been known as an organic semiconductor material due to a high carrier mobility thereof for many years. In addition, “carrier mobility” herein is used in a broad sense, including an electron mobility and a hole mobility.
The polyacene compound is generally unstable to light or oxidization, and therefore is a material group that is difficult to be industrially applied. Therefore, in order to improve chemical stability, a large number of compounds have been studied with regard to a compound wherein various kinds of substituents are introduced into an acene skeleton (see Non-patent literature No. 1, for example) and a compound wherein a chalcogen element such as sulfur and selenium is introduced into a part of acene skeleton, such as dibenzothienothiophene and dinaphtho-thienothiophene (see Patent literature Nos. 1 to 2, for example). The chemical stability of the compounds is improved while the high carrier mobility is maintained. However, as a molecular structure becomes more complicated, the compounds can be barely synthesized by using an expensive raw material and a reactant having a high environmental load, and through multi-step synthesis.
Thus, a variety of organic semiconductor materials have been developed so far, but synthesis of an organic semiconductor material in which both the chemical stability and the high carrier mobility are satisfied has been difficult through an industrially applicable route.
On the other hand, a chalcogen compound such as dinaphthofuran, dinaphthothiophene, dinaphthoselenophene, dianthrafuran, dianthrathiophene and dianthraselenophene can adopt a U-shaped, V-shaped or W-shaped structure depending on a substitution position of a benzene ring, and has an interesting molecular structure from a viewpoint of a degree of freedom of a molecular design. Herein, each structure is shown by taking dinaphthofuran as an example.

A compound having a basic skeleton of the chalcogen compound, namely, an unsubstituted chalcogen compound has been already disclosed (see Patent literature Nos. 3 to 4 and Non-patent literature Nos. 2 to 7, for example), and the compound is excellent in chemical suability and thermal stability. However, no substantial study has been made on utilization as the organic semiconductor material. Patent literature No. 5 discloses an organic semiconductor thin film using dinaphthothiophene having a V-shaped structure (unsubstituted dinaphthothiophene) and a dinaphthothiophene derivative into which 4 to 12 substituents are introduced. However, any semiconductor characteristics are not specifically disclosed, and any compound other than dinaphthothiophene, any compound having a U-shaped structure and any compound having a W-shaped structure are not disclosed.